This invention relates to a system for the purification of water by reverse osmosis.
Reverse osmosis systems are commonly used for removing impurities from water, such as drinking water. A conventional reverse osmosis system includes a reverse osmosis module or filter having a reverse osmosis membrane. Feed water is supplied to the module, and the module delivers filtered product water having a reduced impurity content. Not all of the feed water supplied to the module passes through the reverse osmosis membrane, and this unfiltered water, or brine, is commonly discharged to drain or recycled through the filter or for some other use.
A number of prior art solutions for draining the brine from the reverse osmosis module have been employed. One such solution is to provide a brine drain port on the brine side of the module membrane, with a restrictor to ensure that the feed water permeates the membrane rather than flowing directly through the brine drain port. However, the problem with this solution is that the restrictor frequently becomes clogged, resulting in a build-up of brine in the module and the eventual inoperability of the reverse osmosis system.
Another prior art solution is to provide an unrestricted brine drain port on the brine side of the module membrane, but to include a tap valve thereon, again to ensure that the feed water permeates the membrane rather than simply flowing through the unrestricted brine drain port. Under ordinary circumstances, the tap is closed and product water is produced in the conventional manner, with the brine building up within the module on the brine side of the membrane. However, periodically the tap will be opened to supply unfiltered water for an appropriate purpose, such as laundry, irrigation, a hot water heater, a dishwasher, or the like. Opening the unrestricted tap suspends the creation of purified water, and diverts all of the incoming feed water through the tap, resulting in a high velocity flushing of the brine side of the module. This type of system can work very well, but is subject to uncertainty because of its dependence on the periodic opening of the tap. If the tap isn't opened for a substantial period of time, the system will become clogged with brine and cease operation.
To increase the volume of product water, it is known to employ a pump to increase the pressure of the feed water supplied to the reverse osmosis module. A conventional electric motor driven pump may be used for this purpose. It is also known to employ a reciprocating pump which is driven solely by the feed water, which, for example may be supplied from a city water system and have a pressure of approximately 40-70 psi. In these prior art systems, the piston is typically driven through its pumping stroke by feed water at supply pressure. Then, the piston is driven through its return stroke by a biasing spring in combination with brine from the reverse osmosis module, which has been drained from the module through an unrestricted port and is delivered by a fluid conduit into a return chamber of the pump. The brine drain port is controlled by a valve which is actuated in accordance with the position of the piston, so that product water is produced during the pumping stroke of the piston, with the brine drain valve in the closed position, and brine is drained into the return chamber of the pump during the return stroke, with the brine drain valve open, to assist in returning the piston.